1. Field of the Invention
The present invention relates to DLC film-coated plastic containers suitable to beers, sparkling wines, wines, high-fruit drinks and others that are sensitive to oxygen.
2. Description of the Related Art
In general, plastic containers are easy to form, lightweight and inexpensive, and are therefore widely used as packing containers in various fields of edibles, drinks, medicines, etc.
As well known, however, plastics have the property of passing low-molecular gases such as oxygen, carbon dioxide and others therethrough, and the property of absorbing or adsorbing low-molecular organic compounds. Therefore, as compared with glass containers, plastic containers are often limited for their applications and forms.
For example, in case where plastic containers are used for packing carbonated drinks such as beers and others, or wines, oxygen will penetrate them to time-dependently oxidize the drinks packed in them. In addition, carbon dioxide gas in the packed carbonated drinks will pass through the plastic containers outside them, and the drinks will go flat. Therefore, plastic containers are unsuitable to drinks that must not be oxidized, and to carbonated drinks.
On the other hand, in case where plastic containers are used for packing drinks with flavoring ingredients, such as orange juices and others, the flavoring ingredients of low-molecular organic compounds existing in the drinks (for example, limonene and others in orange juices) will be absorbed or adsorbed by them. As a result, the composition of the flavoring ingredients of the packed drinks will be unbalanced, and the quality of the drinks will become poor. For these reasons, plastic containers are unsuitable to drinks with flavoring ingredients.
The recent tendency in the art is toward recycling natural resources, for which the problem is how to collect and recover used containers. In case where plastics are used for returnable containers and used plastic containers are left as such after they are collected, they will absorb or adsorb various low-molecular organic compounds that will give musty odors. Accordingly, using plastics for returnable containers is limited, being different from the case of using glass for returnable containers.
However, as so mentioned hereinabove, plastic containers have the advantages of easy moldability, light weight and low costs. Using plastic containers for packing carbonated drinks, drinks with flavoring ingredients and the like, or for packing substances that require high purity, or using them as returnable containers, if possible, will be extremely convenient.
To meet the requirements, some techniques such as those mentioned below have been disclosed. Japanese Patent Laid-Open No. 53116/1996 discloses plastic containers with their inner surfaces being coated with a DLC (diamond-like carbon) film. Japanese Patent Laid-Open No. 53117/1996 discloses an apparatus and a method for producing the containers. Japanese Patent Laid-Open No. 258825/1998 discloses an apparatus and a method for producing DLC film-coated plastic containers on an industrial scale. Japanese Patent Laid-Open No. 226884/1998 discloses an apparatus and a method for uniformly coating containers with a DLC film, in which the containers to be coated are so modified that they have branches projecting outward from their outer surfaces.
The DLC film will be referred to as an i-carbon film or a hydrogenated amorphous carbon film (a-C: H) film, including hard carbon films. The DLC film is an amorphous carbon film, having SP3 bonds.
Forming such a DLC film on the inner surfaces of plastic containers will make the resulting plastic containers returnable.